This invention relates to the production of tapes such as tapes comprising a center layer of yttria stabilized zirconia sandwiched between outer layers of strontium doped lanthanum manganite. Such tapes are useful as membrane materials in fuel cells, gas separating devices and the like and specifically in high temperature solid electrolyte fuel cells and high temperature solid electrolyte electrolysis cells herein referred to collectively as "tape-containing devices".
Yttria stabilized zirconia, which for brevity is sometimes referred to herein as "YSZ", is known to be a good material for use in the electrolyte layer in such tape-containing devices. However it has been found that tapes cast using commercially available YSZ powders require a sintering temperature of at least 1400.degree. C. in order to produce a YSZ layer having a density of at least about 95% of theoretical density.
Strontium doped lanthanum manganite, which for brevity is sometimes referred to herein as "LSM", is known to be a good material for use in electrodes produced by tape casting methods. LSM having the mole ratio La.sub.0.8 Sr.sub.0.2 MnO.sub.3 is available as a submicron size material having a surface area of 3 to 5 m.sup.2 /g from HUA Associates, Rolla, Mo. However it has been found that this powder when sintered at 1400.degree. C., or even at 1300.degree. C., forms too dense a layer for use as an efficient electrode material in such tape-containing devices.
Furthermore, green LSM-YSZ-LSM layer tapes when sintered at 1400.degree. C. causes the manganese in the outer layers to migrate into the center YSZ layer thereby adversely affecting the electrical properties of the tape for use in such tape-containing devices.
Accordingly, it would be useful to produce a tape for use in such tape-containing devices that would have a central YSZ layer having at relatively high theoretical density sandwiched between outer LSM layers having a relatively low theoretical density without significant migration of manganese from the outer layers into the central layer.